1. Field of the Invention
The present invention is directed to a syringe. More particularly, the invention relates to a safety syringe which prevents needle-stick injuries unless a biasing force is applied to the plunger thereby to expose a sharp point necessary for penetration of tissue.
2. Related Art
Recently, concerns have been raised over protecting medical personnel from coming into contact with infected equipment. Such concerns have lead to the development of safety syringes which protect or shield the sharp point of the needle when not in use, so as to prevent needle-stick injuries from used syringes.
An example of such a syringe is shown in U.S. Pat. No. 5,088,986 which utilizes a needle sheath which is retractable so as to expose a needle for administering medication. The mechanism used to retract the sheath is relatively complex, relying on a switch device and a spring-loaded mechanism.
U.S. Pat. No. 4,969,877 discloses a syringe having a retractable needle. The syringe includes an outer housing having an inner chamber which is slidable therein, the inner chamber having a needle extending therefrom. The syringe is adapted to lock into a retracted position and into a deployed position forwardly within the housing for injection.
U.S. Pat. No. 4,941,883 discloses a syringe which is somewhat similar to that shown in the '877 patent in that a retractable needle is provided. However, use is made of a reservoir which is parallel to a sheath in which the needle retracts. Fluid communication between the needle and the reservoir is achieved through a radial opening and radial apertures, and separate plungers are used for deployment of the needle and injection of medication. Other safety needle apparatuses are shown in U.S. Pat. Nos. 4,834,718 and 4,507,117.
Each of the state of the art safety needles described above has a relatively complex structure, such as spring-loaded switch mechanisms, to protect the sharp point of the needle. Accordingly, while such syringes attempt to offer increased safety, they are costly to manufacture. Additionally, the prior art safety syringes require additional manipulation of the safety devices to ready them for injecting medication. Accordingly, objectives of the present invention include provision of a simple, easy to use and cost-effective safety syringe which is adapted to prevent needle-stick injuries.